1. Field of the Invention
The present invention is related generally to lasers and more specifically to side-pumped composite laser rods and a mounting structure for increased efficiency of such lasers.
2. State of the Prior Art
Side-pumped solid-state laser rods have an advantage over longitudinal pumped rods in that they are more readily scaled to higher output powers, because they are more conducive to pumping with a plurality of light sources. However, conventional side-pumped rods are often not very efficient absorbers of the pumping radiation, primarily because the rods are fairly transparent and not very thick, so a substantial portion of the radiation from the pump source can pass all the way through the rod without being absorbed. Some pump source radiation can also be lost by reflection from curved lateral surfaces of cylindrical-shaped laser rods, and there can be problems in maintaining TEM.sub.00 mode operation when too much of the pump light that is absorbed by the rods gets absorbed close to the incident surface of the rod. Limited heat dissipation at higher average power operation can also result in serious thermo-optic distortions in the rod due to excessive heat build-up. Physical damage due to stress-fracture may also occur with high heat loads.
There have been several developments to alleviate the problems with side-pumped lasers. For example, G. E. Devlin et al., "Composite Rod Optical Masers," Applied Optics, Vol. 1, No. 1, Jan. 1962, reported the development and testing of a composite rod in which a core of doped, light absorbant gain medium is surrounded by a transparent cladding. This composite structure enhanced radiation absorption in the doped core, and the larger diameter cladding provided increased heat exchange surface area for more efficient heat dissipation to the surrounding environment. R. Byer et al., in their U.S. Pat. No. 4,860,295, issued on Aug. 22, 1989, disclosed improvements in such composite rods, comprising a neodymium doped yttrium aluminum garnet (Nd: YAG) core surrounded by a cladding made of the undoped base material. The undoped base material of the cladding is not absorptive, while the doped core does absorb some of the transversely directed side-pump light and functions as the gain medium. However, the Byer et al. core and cladding materials have the same atomic structure, except for the doping ions in the core, to minimize index of refraction differences between the core and the cladding so that the TEM.sub.00 mode diameter can be greater than the core portion diameter without extensive index of refraction discontinuity, which enhances utilization of absorbed energy. The Byer et al. patent also discloses a reflecting element positioned diametrically opposite the pump light source to reflect the pump light that passes unabsorbed through the rod back into the rod for another opportunity to be absorbed, thereby effectively lowering the threshold energy necessary for laser action.
However, further improvements in pumping efficiency, heat dissipation, and mounting structures are still needed to improve the performance of side-pumped lasers for a multitude of potential commercial applications, such as medical and industrial lasers and transmitter sources for remote sensing.